/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package org.apache.tomcat.jni;

import java.nio.ByteBuffer;

/**
 * Shm
 *
 * @author Mladen Turk
 */
public class Shm {

	/**
	 * Create and make accessible a shared memory segment.
	 * <br>
	 * A note about Anonymous vs. Named shared memory segments:<br>
	 * Not all platforms support anonymous shared memory segments, but in
	 * some cases it is preferred over other types of shared memory
	 * implementations. Passing a NULL 'file' parameter to this function
	 * will cause the subsystem to use anonymous shared memory segments.
	 * If such a system is not available, APR_ENOTIMPL is returned.
	 * <br>
	 * A note about allocation sizes:<br>
	 * On some platforms it is necessary to store some metainformation
	 * about the segment within the actual segment. In order to supply
	 * the caller with the requested size it may be necessary for the
	 * implementation to request a slightly greater segment length
	 * from the subsystem. In all cases, the apr_shm_baseaddr_get()
	 * function will return the first usable byte of memory.
	 *
	 * @param reqsize  The desired size of the segment.
	 * @param filename The file to use for shared memory on platforms that
	 *                 require it.
	 * @param pool     the pool from which to allocate the shared memory
	 *                 structure.
	 * @return The created shared memory structure.
	 */
	public static native long create(long reqsize, String filename, long pool)
			throws Error;

	/**
	 * Remove shared memory segment associated with a filename.
	 * <br>
	 * This function is only supported on platforms which support
	 * name-based shared memory segments, and will return APR_ENOTIMPL on
	 * platforms without such support.
	 *
	 * @param filename The filename associated with shared-memory segment which
	 *                 needs to be removed
	 * @param pool     The pool used for file operations
	 */
	public static native int remove(String filename, long pool);

	/**
	 * Destroy a shared memory segment and associated memory.
	 *
	 * @param m The shared memory segment structure to destroy.
	 */
	public static native int destroy(long m);

	/**
	 * Attach to a shared memory segment that was created
	 * by another process.
	 *
	 * @param filename The file used to create the original segment.
	 *                 (This MUST match the original filename.)
	 * @param pool     the pool from which to allocate the shared memory
	 *                 structure for this process.
	 * @return The created shared memory structure.
	 */
	public static native long attach(String filename, long pool)
			throws Error;

	/**
	 * Detach from a shared memory segment without destroying it.
	 *
	 * @param m The shared memory structure representing the segment
	 *          to detach from.
	 */
	public static native int detach(long m);

	/**
	 * Retrieve the base address of the shared memory segment.
	 * NOTE: This address is only usable within the callers address
	 * space, since this API does not guarantee that other attaching
	 * processes will maintain the same address mapping.
	 *
	 * @param m The shared memory segment from which to retrieve
	 *          the base address.
	 * @return address, aligned by APR_ALIGN_DEFAULT.
	 */
	public static native long baseaddr(long m);

	/**
	 * Retrieve the length of a shared memory segment in bytes.
	 *
	 * @param m The shared memory segment from which to retrieve
	 *          the segment length.
	 */
	public static native long size(long m);

	/**
	 * Retrieve new ByteBuffer base address of the shared memory segment.
	 * NOTE: This address is only usable within the callers address
	 * space, since this API does not guarantee that other attaching
	 * processes will maintain the same address mapping.
	 *
	 * @param m The shared memory segment from which to retrieve
	 *          the base address.
	 * @return address, aligned by APR_ALIGN_DEFAULT.
	 */
	public static native ByteBuffer buffer(long m);

}
